A conventional fire door, as shown in FIG. 1, is opened by pressing a handlebar 11 of a handlebar mount 10 horizontally located in the middle of the fire door, whereby a lock bolt 12d in a lock body 12 is retracted and relieves a locked state that closes and locks the fire door, thereby making the fire door opened. This operation is achieved by a diagonal depression motion of the handlebar 11 which is pressed by a user to move in a downward and diagonal direction. Please refer to FIGS. 2 and 3 which shown the structure of a conventional fire door lock being rotated by 90 degrees to be oriented in a horizontal direction for clear illustration. The handlebar mount 10 houses a handlebar 11 that allows a user to press downwards and a lock body 12 that accommodates a lock bolt 12d. The handlebar 11 is screwed to two horseshoes 13 located at the bottom of the handlebar mount 10. A roller 13b penetrates through two slanted slots 13a respectively formed on two side walls of each horseshoe 13 and is fixed to the side walls of the horseshoe 13 by means of a pin 13c. A pin 13e having a wound elastic member 13d thereon is secured to the bottom of each horseshoe 13, wherein one end of the elastic member 13d is in contact with the bottom of the roller 13b on which an upward compression force is exerted. Under a normal condition, the pin 13c of the roller 13b holds the handlebar 11 in position at the top of the handlebar mount 10. When the user exerts a force on the handlebar 11, the roller 13b is pushed downwards and travels along the slots 13a of each horseshoe 13 by the force, thereby inducing diagonal translocation of the handlebar 11 in the handlebar mount 10. The lock body 12 located at the front of the handlebar mount 10, shown in FIG. 3, comprises a seesaw lever 12a which is constructed by coupling a push part 12b and a pull part 12c, wherein the push part 12b is in contact with an inside surface of the handlebar 11 and the pull part 12c is engaged with a cavity 12e formed by the lock bolt 12d in the lock body 12. When the user presses the handlebar 11, the push part 12b of the lever 12a is pushed downwards while the pull part 12c is moved upwards. At the same time, the pull part 12c comes into contact with the lock bolt 12d which is driven to rotate in a counterclockwise direction, making the lock bolt 12d retracted into the lock body 12 to facilitate a door opening action.
In view of the above door opening operation in the use of the conventional fire door lock, although the user presses the handlebar 11 in a manner as illustrated by the arrow in FIG. 3, the handlebar 11 is moved in a diagonal direction by the roller 13b travelling along the slots 13a of each horseshoe 13 in the handlebar mount 10. The diagonal movement of the handlebar 11 is composed of a vertical movement and a horizontal movement. And the force exerted by the user is undesirably divided into two components: a force vertical to the push part 12b and used for operating the lock bolt 12d, and a force horizontal to the push part 12b and having no contribution to the lock bolt 12d, which therefore requires a larger amount of force exerted by the user due to wastage. Further, the horizontal movement of the handlebar 11 makes the travel direction of the handlebar 11 different from that of the hands of the user, which causes discomfort to the hands of the user when operating the door lock.
Furthermore, when the lock bolt 12d of the conventional fire door lock is extended from the lock body 12, as shown in FIG. 1, the lock bolt 12d is inserted into a catch 14 which has an opening for accommodating the lock bolt 12d and which is adhered to a surface of a door frame of the fire door. However, the catch 14 protrudes outwardly from the surface of the door frame and thus distorts the overall appearance. Moreover, the exposed catch 14 is easily subject to damage from vandals. Therefore, a novel fire door lock which can eliminate the above drawbacks is greatly desired.